Epigraphs are like little appetizers to the great entrée of a story. They illuminate important aspects of the story, and they get us headed in the right direction.
"Fairy tales are more than true: not because they tell us that dragons exist, but because they tell us dragons can be beaten."
– G.K. Chesterton
First, let's introduce G.K. Chesterton, who lived from 1874 to 1936. Chesterton was a British author, philosopher, journalist, playwright, debater... the dude was busy. He wrote everything from detective novels to fantasy books and he was great student of literature (he was a Shmoop fan before Shmoop even existed!). So that's G.K. Now let's see what he's talking about.
When Chesterton writes about "dragons," he doesn't mean actual dragons. At least not completely. Instead, dragons represent any evil thing that seems impossible to beat. The great thing about fairy tales is that they give us the courage to overcome even the toughest obstacles (like, say, dragons) – because of fairy tales, we know it can be done.
Why is this important for Coraline? Well, Coraline is a sort of fairy tale: the leading lady goes into another world and has to fight against evil forces. Despite the odds against her, Coraline doesn't give up. And in the end, she beats the "dragon" in her life: the evil other mother.